Cardiac late potentials are those signals which occur at the end of the QRS complex and usually extend into the ST segment. High resolution ECG technology, including signal averaging and high pass filtering, is necessary for recording these potentials on the body surface. Late potentials have been shown in numerous clinical studies to be a strong predictor of ventricular arrhythmias following myocardial infarction. Only a few animal studies have been done which underpin some of the methodology and conclusions drawn in these clinical studies. We have used a canine myocardial infarction model which produces late potentials to study and compare their appearance on the body surface and the epicardial surface. As our original studies progressed many questions arose surrounding the quantification of the signals on the epicardial surface of the heart. These problems center around electrogram analysis and the generation of isochronous maps. Accurate identification of activation and the problems associated with interpolation to generate a map must be solved before the forward solution linking both milues can proceed. We have defined 5 specific aims: 1) Determine improved methods for identifying a unique activation time from extracellular electrograms recorded from infarcted and damaged regions of the ventricles. 2) Develop the criteria for generating accurate maps of activation within and surrounding infarct regions of the ventricles. 3) Expand the thin layer biophysical model to include more realistic components of the damaged myocardium. 4) Develop a spatial sampling theorem for cardiac mapping. 5) Determine the features of body surface potentials which reflect important properties of the viable tissues within the damaged and infarcted myocardium. The long term goal of establishing the fundamental bases for cardiac late potentials remain and the specific aims outline a plan to reach this goal. We have emphasized that many of the solutions which exist for electrogram analysis and map generation do apply to damaged/infarcted regions of the heart. We will continue to use in vitro data with biophysical models to further enhance our approach to analyzing cardiac late potentials.